I only have a couple minor corrections.

Large frame track tension was maintained by a big old spring. You de-tension by adding oil to one side of the cylinder and compressing the spring. When you are ready to put it back to work, you release the oil pressure in the cylinder and let the spring do it's thing.

There was a model 70 made for a short time. It was essentially a 75 with the 3306 65 engine. Was mostly intended for low speed heavy pull operations.